This deep image shows the nebula (cyan) spanning 2 million light years and discovered around the bright quasar UM287 (in the center of the image). The energetic radiation of the quasar makes the surrounding intergalactic gas glow and reveals the morphology and physical properties of a cosmic web filament. The picture was taken at the WM Keck observatory. Photo credit: S. Cantalupo, UC Santa Cruz
Astronomers have discovered a distant quasar that illuminates a giant nebula of diffuse gas, revealing, for the first time, part of the filament network believed to connect galaxies in a cosmic web. Researchers from the University of California at Santa Cruz led the study, published January 19 in Nature.
Using the 10-meter Keck-I telescope at the WM Keck Observatory in Hawaii, the researchers discovered a very large, glowing gas nebula that extends over 2 million light years across intergalactic space.
“This is a very extraordinary object: it is huge, at least twice the size of any previously discovered nebula, and extends far beyond the galactic environment of the quasar,” said first author Sebastiano Cantalupo, a postdoctoral fellow at UC Santa Cruz.
The standard cosmological model of structure formation in the universe predicts that galaxies are embedded in a cosmic web of matter, most of which (about 84 percent) is invisible dark matter. This web can be seen in the results of computer simulations of structural evolution in the universe, showing the distribution of dark matter on a large scale, including the dark matter halos in which galaxies form and the cosmic web of filaments connecting them. Because of gravity, ordinary matter follows the distribution of dark matter, so filaments of diffuse, ionized gas are expected to follow a pattern similar to that in simulations of dark matter.
However, these filaments have never been seen before. Intergalactic gas has been detected by absorbing light from bright background sources, but these results do not show how the gas is distributed. In this study, the researchers discovered the fluorescent glow of hydrogen gas that results from its illumination by intense radiation from the quasar.
Computer simulations suggest that matter in the universe is distributed in a “cosmic web” of filaments, as can be seen in the picture above from a large-scale simulation of dark matter (Bolshoi simulation by Anatoly Klypin and Joel Primack). The inset is an enlarged, high-resolution image of a smaller portion of the cosmic web, 10 million light years in diameter, from a simulation that contains both gas and dark matter (Photo credit: S. Cantalupo). The intense radiation of a quasar can illuminate part of the surrounding cosmic web (highlighted in the picture) like a flashlight and light up a gas filament, as was observed in the case of the UM287 quasar. Photo credits: Background image: A. Klypin and J. Primack; Inset: S. Cantalupo
“This quasar illuminates diffuse gas on scales that go far beyond the previous ones and gives us the first picture of an extended gas between galaxies. It offers an excellent insight into the overall structure of our universe,” said co-author J. Xavier Prochaska. Professor of Astronomy and Astrophysics at UC Santa Cruz.
The hydrogen gas illuminated by the quasar emits ultraviolet light known as Lyman Alpha radiation. The distance to the quasar is so great (about 10 billion light years) that the expansion of the universe “stretches” the emitted light from an invisible ultraviolet wavelength to a visible shade of purple when it reaches the Keck telescope. Knowing the distance to the quasar, the researchers calculated the wavelength for Lyman alpha radiation from that distance and built a special filter for the telescope’s LRIS spectrometer to get an image at that wavelength.
“We examined other quasars this way without discovering such extensive gas,” said Cantalupo. “The light from the quasar is like a flashlight beam, and in this case we were fortunate enough to have the flashlight pointing at the nebula and lighting the gas. We think this is part of a filament that may be even longer than this . but we only see the part of the filament that is illuminated by the beam emission of the quasar. “
A quasar is a type of active galactic nucleus that emits intense radiation powered by a supermassive black hole in the center of the galaxy. In an earlier study of distant quasars, using the same technique to search for glowing gas, Cantalupo and other so-called “dark galaxies” discovered the densest gas nodes in the cosmic web. It is believed that these dark galaxies are either too small or too young to form stars.
“The dark galaxies are much denser and smaller parts of the cosmic web. In this new image we see dark galaxies as well as the much more diffuse and extensive nebulae,” said Cantalupo. “Some of this gas will fall into galaxies, but most of it will remain diffuse and never form stars.”
The researchers estimated the amount of gas in the fog to be at least ten times the expected results from computer simulations. “We believe that there may be more gas in small, dense clumps in the cosmic web than in our models. These observations challenge our understanding of intergalactic gas and give us a new laboratory to test and refine our models,” said Cantalupo.
Dark galaxies of the early universe were discovered for the first time
Article: dx.doi.org/10.1038/nature12898 Provided by the University of California – Santa Cruz
Quote: Distant quasar illuminates a filament of the cosmic web (2014, January 19), retrieved from https://phys.org/news/2014-01-distant-quasar-illuminates-filament-cosmic.html on December 25, 2020 has been
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